It's useful to link the two developments because the two cases are so very different. Mayor Livingstone first ran London when he ousted Andrew (now Lord) McIntosh in the Labour group in 1981, a career of almost French durability.

Brown has been prime minister since only last June, though he was first elected an MP in 1983 and has also been around a long time as chancellor.

But politicians run out of road and run out of luck. The tide of public sentiment turns (there's boredom too, as well as disaffection), as it did against Labour in 1978-79 and against the Tories after Black Wednesday in September 1992.

Does it mean both regimes are finished? Not necessarily. Again the comparison is instructive. Brown is a backstairs operator, happier exercising power out of view. Livingstone is a street fighter, one of the best, as the LSE's authoritative Tony Travers reminded readers of the heavily-biased London Evening Standard after it gleefully reported Boris Johnson's 49-37-12% lead over Livingstone and the Lib Dem candidate, ex-copper Brian Paddick, as the formal campaign for mayor begins.

That's another difference. London will vote in this surrogate general election in just 45 days, the wider electorate perhaps not for two years. Asking Londoners to re-elect Livingstone - indeed anyone - after eight years in power is asking a lot. He's done some good things and some bad things, but he's 62 (four months older than me) and we all lose the plot in the end. But he won't give up and he has a bonus in Boris.

The challenger is finally getting serious about policy and he now has good handlers. He's not the crypto-fascist some critics foolishly claim, but he's still Boris and he could still blow that lead by a spectacular howler that crystalises the mayor's complaint that he's too much of a flake to be allowed anywhere near the helm of a great world city.

Last week Boris's nostalgic pledge to restore Routemaster buses, costed at £8m, turned out to be wrong by £100m. There were two paragraphs to that effect at the end of an Evening Standard article.

Led by Andrew " Sexed Up" Gilligan - a journalist whose ego could also blow it - the Standard has been campaigning against sort-of-corruption at City Hall with all the zeal of its big brother, the Daily Mail.

But the paper's activism can't save Boris if he commits a major gaffe Londoners can't ignore. At last Boris, who is clever enough to have winged his way through life, faces a disciplined challenge under pressure. They may have to chloroform him as polling day approaches.

Obviously, that's not Gordon Brown's problem; quite the reverse. Events are piling up against Labour at every level, not least of all the global financial crisis. And Brown is an introvert who finds the public leadership business difficult.

As we all now know (and Tony Blair knew very well) he hesitates when he should be decisive. Boris's more disciplined fellow-Etonian, David Cameron, who knows he risks brand contamination from Boris's antics, has problems of his own. But he is making few mistakes.

Yet Brown has the huge advantage of experience and weight. It's up to him to pull it back. My line on the Blair succession was always that there never was a realistic alternative: Brown was Labour's destiny, for better or worse. We'd only know which it would be when it happened. It's now happening.

Is it over yet? Of course not. The public mood is jittery and fickle. Voters do not like Alistair Darling's budget. But as every ex-chancellor can confirm (I have been speaking to several) early verdicts on budgets can be poor guides.

ICM's findings today suggest that even Labour heartland voters are wavering. But there's still a long way to go.

And before any reader shouts ''special pleading'' let me remind him (it's always a him) that back in 1992 most of the polls and the pundits had written off John Major, many in dismissive terms. Labour's poll lead was 7% at one point.

My hunch was otherwise and on eve of poll I urged the paper to entertain the possibility of a Tory victory. While our four broadsheet rivals all opted for ''It's too close to call'' and "It's neck and neck'' headlines on polling day - April 9 - the Guardian's said: ''Late surge gives Tories hope.'' Will it happen again? I don't know. It's too soon to say.